Objective: To use an analog computer to simulate dynamic biological systems for greater understanding of their behavior. Approach: A medium-sized general purpose analog computer is maintained and operated for the use of all the clinical and basic science departments of the Division of Biological Sciences. The computer has 76 operational amplifiers programmable as integrators or summers, 110 coefficient potentiometers, 30 multipliers and 8 arbitrary function generators. Two of the multipliers are fast, high accuracy quarter-square units. Eight removable patch boards are available for programming and storing problems. A precision X-Y plotter, fast eight-channel oscilloscope or eight-channel direct writing oscillograph are available for readout. A seven-track FM tape recorder with tape loop attachment is available for input of tape recorded data. It is portable and may be taken to the laboratory to record data. The computer laboratory is operated as an open-shop facility with problems accepted on a first-come, first-served basis. Problems that have been or are under investigation include properties and responses of viscoelastic tissues, neural net similations, active transport through membranes, modulation transfer functions of imaging systems, enzyme kinetics, radiation treatment planning, kinetics of self-renewing cell populations and development of numerous on-line data processing systems. Instruction in computer programming and operation is offered in a lecture and laboratory course given at frequent intervals.